Acoustical device



Nov. 27, 19 34. I v R. H. MARRIOTT 1,981,962

ACOUSTICAL DEVICE Filed June 29. 1933 Patented Nov. 27, 1934 UNITED STATE-S PATENT 1 OFFICE oons-11cm. DEVICE 1mm 11. minim, Brooklyn, N. Y. Application June 29, 1933, Serial No. 678,115

10 Claims. '(Cl. 181-31) This invention relates to an acoustical device and has for its object the improvement of soundquality and sound distribution, of loud speakers aricl other sound amplifiers.

5 In the present day loud speaker, the diaphragm acts to compress air in front of a baflie box and rarify air within the box and vice versa, at the frequency of the electric current used to drive the diaphragm or within the limits of the ability of the diaphragm to follow such frequencies. The diaphragm ordinarily forms part of the front of the box and, as combined, the box-diaphragm combination has a natural period'and this is also true of the air in the box,

which. is usually more or less open at the back and has a natural period. As a result, notes .having frequencies equal to these natural periods are greatly exaggerated. Driving currents of the impulse or highly damped type, cause the box 20,.and air in the box to vibrate at their natural periods, producing the characteristic sounds of the loud speaker which have a peculiar objectionable quality unlike the sounds that should be reproduced. A further cause of unnatural reproduction is that the diaphragm difi'ers so greatly from the numerous musical devices like reeds, horns, strings and sounding boards that its characteristics will not permit it to reproduce all of their characteristics. It is also well known that the box-diaphragm combination does not reproduce the frequencies of the musical instruments at the relative volumes at which those frequencies were originally, produced by the instruments. Between the deficiencies of the boxdiaphragm combination and the devices andcircuits used to deliver the electric currents, low notes reproduced by the speaker are not as loud as they shouldbe. Also some of the high fundamental frequencles and harmonics are either lost or reproduced too weakly. Also with the common loud speaker, sound produced gives the impression of being projected in a single beam from a hole in the front of the box, thus differing from the original sounds which are entirelv free of this peculiar quality.

Instead of providing a box around the diaphragm to-serve as a baflle, I use a structure that provides bames and also provides air columesand walls properly proportioned to consoserve and relatively enhance frequencies and notes that are reproduced too weakly and effect such distribution of the sound as to give a pleasing and natural effect.

Several constructions suitable for carrying my invention into eflect are illustrated inthe accompanying drawing but I do not wish to be understood as intending to limit myself to the same, as various changes may be made therein or other forms used without departing from the spirit and scope of the invention as outlined in the appended claims.

In the drawing,

Fig. 1 is an overall view in elevation of an acoustical device, constructed in accordance with the general principles of my invention;

Fig. 2 is a central vertical section of the lower end of the acoustical device shown in Fig. 1, the section being indicated as taken on line s'-s of Fig. 3;

Fig. 3 is a transverse section on the line 10 s-s of Fig. 1; 1

.Fig. 4 is a similar view on the line s-s of Fig. 1;

Fig. 5 is a central vertical sectional view of a modified arrangement of long and short air columns about a single diaphragm, and v Fig. 6 is a cross sectional view of Fig. 5, taken on the line s*-s thereof. Y

Referring to Fig. 1 and Figs. 2, 3 and 4 which are sections of Fig. 1, the usual flexible edge of 30 diaphragm 100, is shown in contact with the lower edge of a cylindrical wall 101. Preferably attached to the inner surface of wall 101, and to each other, there is a circle of round pipes 2. Between the outside of the pipes 2, and the 111-: B5

side of the wall 101, air columns 3, are formed.

Radial walls 5, form the sides of the angles subtended by the pipes 2, in the circle and as assembled those radial walls 5, and the pipes 2, form the sides of air columns 1. The pipes 2, are of different lengths and the lengths of the radial walls 5, conform to the lengths of the pipes 2, to provide air columns 1, of the same lengths as the pipes 2. Air columns 1, are closed at the top and pipes 2, are open atthe top. The cylindrical wall 101, is .cut spirally at the top from 102 to 103, making air columns 3, of different lengths. The lower ends of the pipes and air columns 1 and 3 are open and diaphragm 100, shows all of the pipes 2, and the 5 air columns 1 and 3. Fig. 4, a cross section near the top of Fig. 1, shows the pipes 2, and air columns 1, that extend above that point and the wall that closes \the top of an air column 1. With this arrangement, 12 closed and 24 no open air columns are provided above the diaphragm 100.

As is well known, an open air column provides minimum impedance for the sound wave that is twice as long as the air column and a closed air column, such as 1, for example, will reflect a soundwave that is four times its length, back to the diaphragm 100, in phase, to increase the amplitude of that sound. By making the lengths of the 12 closed air columns 1, equal to one fourth the lengths of the sound waves of the notes in the lowest octave that is reproduced by the diaphragm, such low notes are built up. The open pipes 2, of the same lengths ofier the least impedance to the next higher octave. Air columns 3, are half as long as the pipes and offer minimum impedance to the next higher octave.

Air columns 3, are not as large in cross section as the pipes 2, because they are shorter and because the diaphragm reproduces this octave with relatively greater amplitude as a rule.

The method and principles I employ are shown adapted in the drawing in'a simple manner to the usual characteristics, type and shape of the driving element or diaphragm that is used in loud speakers and to the probable available space. Open air columns of twice the length of the closed columns 1, could be used to advantage where suitable space is available. As will be apparent, the same principles may be carried out using air columns in other shapes, other sizes, other numbers and other groupings.

In the modification shown in Fig. 5, the usual loud speaker magnet arrangement is indicated at 111 and diaphragm at 100. 10 indicates closed air columns. 3 and 20 indicate open air columns. The air columns 10 and 20 may be shorter than the wave lengths of the higher notes in the musical scale. The air columns 20, have minimum impedance for the high notes and harmonics above the musical scale. The closed air columns 10, are resonant to similar high sound frequencies and help to build up such sounds to greater amplitudes. Air columns 20, above the diaphragm, outlet in a relatively large and expanding air chamber between the walls 107 and 108. Pivoted at 200, is a reflector and damper having a hard reflecting side 202,

- Fig. 5, sound is reflected upward. When the end 203 is turned to 204, sound is reflected outward. When the end 203, is turned to 205 as in Fig. 6, sound is absorbed by the side 201. The amount to which it is desirable to provide for the building up or picking-out of high frequencies depends upon the diaphragm and other factors. The diaphragm may reproduce high frequencies nearly well enough. Some music may' contain more high sounds than the listener likes. Static when the speaker is used for radio reproduction, may produce a high frequency noise level that makes it desirable to turn the damper to absorb high frequencies or to reflect them toward the ceiling. 110 is a reflecting surface that may be incorporated to deflect sound outward from the bottom of the diaphragm.

Fig. 6 is a cross sectional view of Fig. 5, shows long air columns 1, 2 and 3 and walls 5 and 101, such as are shown in Figs. 1, 2, 3 and 4, arranged about the outlet space between the walls 107, 108 and 101, in Fig. 5 and between the walls 107, 101, 112 and 113 in Fig. 6. The absorbing side 201 and the reflecting side 202 of the reflector and damper is indicated in Fig. 5.

Arefiector and or damper may be included to regulate the output of any air column or of the diaphragm. I

When a diaphragm is mechanically connected to another structure or magnetically connected to that structure or, connected to that structure via sound waves in air, more or less of its vibrations will be repeated, in that structure. If the materials in the structure are properly proportioned and are like the materials in musical instruments, the structure will have some of the harmonic characteristics of the musical instruments. A properly selected amount of such characteristics can contribute to the naturahiess of reproduction. In a sense, a loud speaker may be considered as a musical instrument that will reproduce sounds within the limits of its characteristics and may produce sounds that did not exist in the original. If the structures shown in Figs. 1 to 6, the radial walls 5, are edge-grain spruce, they will vibrate to bring out the harmonic characteristics of the edge-grain spruce sounding boards of pianos, violins and other stringed instruments. If those radial walls 5, are more like leather they will have a tendency to bring out drum sounds. 1f the pipes are like horn pipes they will bring up horn characteristics. In a structure of this kind, material and dimensions may be chosen to cover many of the harmonic characteristics of all sound producers that a loud speaker will be normally called upon to reproduce. The walls of the air columns are also bafliesand may also be vibrating producers of desired sound. Therefore a) great range of sounds and sound combinations may be reproduced by this structure and outleted not only at the diaphragm and at the different locations of the ends of the open air columns but also from numerous surfaces of the structure.

Having thus described my invention, what I claim is:

'1. An acoustical device comprising a producing source of sounds of different frequencies and an assembly of resonators associated with the source of sounds, the said resonators being differently proportioned so that each is limited to respond to its resonant frequently only certain of said resonators being formed by the spaces between the outer walls of the main assembly and the inner wall of an assembly enclosing member. 1

2. An acoustical device comprising a producing source of sounds of diflerent frequencies, a grouped assembly of associated resonators, certain of the resonators offering minimum impedance to sounds of frequencies to which they are resonant, and other resonators of the assembly acting to reflect sounds of their resonant frequencies, back to the source for further ampliflcation of such sounds and an outer member surrounding the grouped assembly in such relation as to form an additional series of resonators.

3. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators made up of two groups, one group offering. minimum impedance to sounds of frequencies to which they are resonant, and the other group acting to reflect sounds of their resonant frequencies back to the source for further amplification of such sounds, and an outer member encircling the assembly and relatively associated therewith to form a third group of resonators.

4. An acoustical device comprising a producing source of sounds of difierent frequencies, an

quencies to which they are resonant and the other group being resonant to low frequencies only and acting to reflect sounds of such frequencies back to the source for increasing their amplification, and an outer member encircling the assembly and relatively associated therewith to form a third group of resonators.

5. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators 'consisting of a large group and a small group,

the ,large group offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the small group being resonant to low frequencies only and acting to reflectsounds of such frequencies back to the source for increasing their amplification, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of a cylindrical casing.

6. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators consisting of two groups of pipes, one group being open pipes and offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes resonant to low frequencies only and acting to reflect'sounds of such frequencies back to the source for increasing their amplification, and a third group of resonators encircling the assembly and formed between the outer walls "thereof and the inner wall of a cylindrical casing.

7. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators consisting of two groups of pipe, one group being open pipes of different lengths oflering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes of different lengths resonant to low frequencies only, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of a cylindrical casing.

8. An acoustical device comprising aproducing source of sounds of difierent frequencies, an assembly of associated resonators consisting of two groups of pipes so relatively arranged that a one group encircles the other, one of the groups being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes of different lengths resonant to low frequencies only, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of'a cylindrical casing.

9. An acoustical device comprising a producing source of sounds of different frequencies, and an assembly of associated resonators consisting of two groups of pipes so relatively arranged that one group encircles and forms part of the wall of the other group, the encircling group being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the encircled group being closed pipes of different lengths resonant to low frequencies only.

10. An acoustical device comprising a producing source of sounds of different frequencies, and an assembly of associated resonators consisting of two groups of pipes so relatively arranged that one group is twice encircled by the other group, the encircling group being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the encircled group being closed pipes resonant to low frequencies only.

ROBERT H. MARRIO'I'I.

crnrmcarr or CORRECTION.

Patent No. 1,981, 962.

November 27, 1934.

ROBERT a. muuuorr.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page 2, line 122, claim 1. for

'-"frequently" read frequency; and that the said Letters Patent sho ld b correction therein that the same may conform to v u e read wlth this Office.

(Seal) I Leslie Frazer Acting Commissioner of Patents.

the record of the case in the Patent quencies to which they are resonant and the other group being resonant to low frequencies only and acting to reflect sounds of such frequencies back to the source for increasing their amplification, and an outer member encircling the assembly and relatively associated therewith to form a third group of resonators.

5. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators 'consisting of a large group and a small group,

the ,large group offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the small group being resonant to low frequencies only and acting to reflectsounds of such frequencies back to the source for increasing their amplification, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of a cylindrical casing.

6. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators consisting of two groups of pipes, one group being open pipes and offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes resonant to low frequencies only and acting to reflect'sounds of such frequencies back to the source for increasing their amplification, and a third group of resonators encircling the assembly and formed between the outer walls "thereof and the inner wall of a cylindrical casing.

7. An acoustical device comprising a producing source of sounds of different frequencies, an assembly of associated resonators consisting of two groups of pipe, one group being open pipes of different lengths oflering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes of different lengths resonant to low frequencies only, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of a cylindrical casing.

8. An acoustical device comprising aproducing source of sounds of difierent frequencies, an assembly of associated resonators consisting of two groups of pipes so relatively arranged that a one group encircles the other, one of the groups being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the other group being closed pipes of different lengths resonant to low frequencies only, and a third group of resonators encircling the assembly and formed between the outer walls thereof and the inner wall of'a cylindrical casing.

9. An acoustical device comprising a producing source of sounds of different frequencies, and an assembly of associated resonators consisting of two groups of pipes so relatively arranged that one group encircles and forms part of the wall of the other group, the encircling group being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the encircled group being closed pipes of different lengths resonant to low frequencies only.

10. An acoustical device comprising a producing source of sounds of different frequencies, and an assembly of associated resonators consisting of two groups of pipes so relatively arranged that one group is twice encircled by the other group, the encircling group being open pipes of different lengths offering minimum impedance to sounds of medium and high frequencies to which they are resonant, and the encircled group being closed pipes resonant to low frequencies only.

ROBERT H. MARRIO'I'I.

crnrmcarr or CORRECTION.

Patent No. 1,981, 962.

November 27, 1934.

ROBERT a. muuuorr.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page 2, line 122, claim 1. for

'-"frequently" read frequency; and that the said Letters Patent sho ld b correction therein that the same may conform to v u e read wlth this Office.

(Seal) I Leslie Frazer Acting Commissioner of Patents.

the record of the case in the Patent 

